A PC steel wire is mainly used for tendon of prestressed concrete to be used for civil engineering and building structures. Conventionally, a PC steel wire is produced by subjecting piano wire rods to a patenting treatment to form a pearlite structure, and thereafter performing wire-drawing and wire-stranding, and subjecting the obtained wire to an aging treatment in a final process.
In recent years, to decrease working costs and reduce the weight of structures, there is a demand for a high-strength PC steel wire having a tensile strength of more than 2000 MPa. However, there is the problem that delayed fracture resistance characteristics decrease accompanying enhancement of the strength of a PC steel wire.
Technology that has been proposed for improving the delayed fracture resistance characteristics of a PC steel wire includes, for example, as disclosed in JP2004-360005A, a high-strength PC steel wire in which, in a region to a depth of at least 1/10d (d represents the steel wire radius) of an outer layer of the steel wire, the average aspect ratio of plate-like cementites in pearlite is made not more than 30. Further, in JP2009-280836A, a high-strength PC steel wire is proposed in which, to make the tensile strength 2000 MPa or more, when the diameter of the steel wire is represented by D, the hardness in a region from the surface to a depth of 0.1D is made not more than 1.1 times the hardness in a region on the inner side relative to the region from the surface to a depth of 0.1D.